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Abstract

Background

Ki67 labeling index (Ki67 LI), the percentage Ki67 immunoreactive cells, is a measure
of tumor proliferation, with important clinical relevance in breast cancer, and it
is extremely important to standardize its evaluation.

Aim

To test the efficacy of computer assisted image analysis (CAIA) applied to completely
digitized slides and to assess its feasibility in routine practice and compare the
results obtained using two different Ki67 monoclonal antibodies.

Materials and methods

315 consecutive breast cancer routinely immunostained for Ki-67 (223 with SP6 and
92 with MM1 antibodies previously examined by an experienced pathologist, have been
re-evaluated using Aperio Scanscope Xs.

Results

Mean human Ki67 LI values were 36%± 14.% and 28% ± 18% respectively for SP6 and MM1
antibodies; mean CAM Ki67 LI values were 31%± 19% and 22% ± 18% respectively for SP6
and MM1. Human and CAIA evaluation are statistically highly correlated (Pearson: 0.859,
p<0.0001), although human LI are systematically higher. An interobserver variation
study on CAIA performed on 84 cases showed that the correlation between the two evaluations
was linear to an excellent degree.

Discussion

Our study shows that a) CAIA can be easily adopted in routine practice, b) human and
CAIA Ki67 LI are highly correlated, although human LI are systematically higher, c)
Ki67 LI using different evaluation methods and different antibodies shows important
differences in cut-off values.